1. Field of the Invention
The present invention relates to a glass composition used as matrix glass for glass doped with dispersed CdS.sub.x Se.sub.y Te.sub.z (x+y+z=1) microcrystallites used as a nonlinear optoelectronic material, a sharp cut filter glass material or an infrared-transmitting filter glass material.
2. Prior Art
The third order nonlinear characteristic in sharp cut filter glass containing about 100 .ANG. CdS.sub.x Se.sub.y (x+y=1) semiconductor microcrystallites dispersed in matrix glass was measured in 1983 (J. Opt. Soc. Am. Vol. 73, No. 5, pp 647-653 (1983). Since that time, public attention has been directed to glass doped with dispersed microcrystallites as a nonlinear optoelectronic material adapted for optical switches, optical computers, etc.
In this type glass doped with dispersed microcrystallites, the dispersion of the energy band caused by a quantum confinement effect is observed. The explanation given to this phenomenon is that the third order nonlinear characteristic is increased by a band filling effect or an exciton confinement effect (for example, as described in a Japanese periodical "Kogaku" Vol. 19, No. 1, pp 10-16 (January 1990)).
In a process of producing this type glass doped with dispersed microcrystallites, in general, silicate glass or borosilicate glass is used as matrix glass. This type glass doped with dispersed microcrystallites, using these kinds of glass as glass matrix, is produced by a method (in general, called "melting method") comprising the steps of: heating and melting a mixture containing starting raw materials for these kinds of glass and starting raw materials for microcrystallites to form a glass melt; cooling the glass melt to room temperature to prepare glass containing constituent elements of the microcrystallites dissolved as ions in the glass matrix; and heating the resulting glass from room temperature to a predetermined temperature and applying heat treatment at the predetermined temperature to the glass to precipitate microcrystallites.
In the case where glass doped with dispersed microcrystallites is produced by the conventional melting method with silicate glass or borosilicate glass as matrix glass, the solubility in the matrix glass, of S, Se and Te components as constituent elements of microcrystallites is very low and these components volatilize during the step of heating and melting the starting raw materials to prepare glass containing constituent elements of microcrystallites dissolved in the matrix glass. Accordingly, even if large amounts of the staring raw materials for microcrystallites are added to the glass raw materials, the concentration of the S, Se and Te components in the glass cannot be increased. Accordingly, the concentration of microcrystallites precipitated by heat treatment is limited to a value lower than 5 wt % (volume percent of microcrystals: 2 vol %), as described in Japanese Patent Postexamin. Publication No. Sho-48-8561.
In the case where a nonlinear optoelectronic element for optical switches, optical computers, etc. is produced by using the glass doped with dispersed microcrystallites produced by the conventional melting method, the value (.chi..sup.(3)) of nonlinear susceptibility expressing the magnitude of the third order nonlinear characteristic is not higher than 10.sup.-8 esu, because it is proportional to the volume percent of microcrystallites in the glass doped with dispersed microcrystallites as described in the above "Kogaku" Vol. 19, No. 1, pp 10-16 (January 1990), thereby making it difficult to operate the nonlinear optoelectronic element through the intensity of light from a semiconductor laser. Further, in the case where a thin sharp cut filter or an infrared-transmitting filter is produced, the rising of the light absorption curve is broad and has a gentle slope, thereby making it difficult to attain reduction in thickness of the optical filter while keeping the characteristic of the optical filter.
The present invention has been attained to solve the aforementioned problems in the conventional glass doped with dispersed microcrystallites as a nonlinear optoelectronic material and an optical filter material, and it is a first object thereof is to provide a matrix glass composition in which the solubility of microcrystallites is high.
It is a second object of the present invention to provide glass doped with dispersed microcrystallites, which contains a high concentration of CdS.sub.x Se.sub.y Te.sub.z (x+y+z=1) microcrystallites.